The present invention relates to an image forming apparatus, such as a copier, a facsimile, a printer, etc., and a post processing apparatus, which is directly or indirectly coupled to the image forming apparatus, and specifically relates to a paper sheet conveyance apparatus, which separates an overlap paper sheet from a regular paper sheet to be conveyed, when an overlapping conveyance error occurs during a conveying operation of the paper sheets accommodated in the apparatus.
Conventionally, as the abovementioned kind of paper sheet conveyance apparatus, which separates the overlap paper sheet from the regular paper sheet to convey it, there has been well-known a paper sheet conveyance apparatus, which is provided with an electrostatic charge generating device or a suction fan, serving as an adsorption devise, disposed in the conveyance path so as to prevent the overlapping conveyance error (for instance, set forth in the Patent Document 1, namely, Tokkaihei 6-32498, Japanese Non-Examined Patent Publication). Referring to the drawing, this conventional apparatus will be detailed in the following.
FIG. 7 shows a schematic diagram of a rough configuration of a conventional separating conveyance apparatus. Referring to FIG. 7, the conventional separating conveyance apparatus will be detailed in the following. The paper sheets 2 are accommodated in the paper sheet feeding section 1, so that the paper sheets 2 are picked up one by one by the paper sheet feeding roller 3, and separated for every paper sheet by means of the separation nail 4 so as to feed a single paper sheet one by one. Further, the upper guide plates 11a, 11b, and the lower guide plates 15a, 15b are disposed between the pair of conveyance rollers 5 and the pair of registration rollers 7, so as to form the conveyance path 17. The upper guide plates 11a, 11b are divided into the upstream section 11a and the downstream section 11b, so that the electrostatic charge generating device 12 can be disposed between the upstream section 11a and the downstream section 11b, so as to exert the electrostatic force onto the paper sheet conveyed through the conveyance path 17. The area located below the electrostatic charge generating device 12 and between the lower guide plates 15a, 15b is opened, so as to form the overlap paper sheet conveying path 18, which is extended toward the lower side. The paper sheet 2 is conveyed by the pair of conveyance rollers 5 including the two rollers 5a and 5b disposed in front of the paper sheet feeding section 1. The paper sheet 2 conveyed by the pair of conveyance rollers 5 is guided by the upper guide plate 11a and the lower guide plate 15a. When the paper sheet 2 arrives at a position in the vicinity of the electrostatic charge generating device 12, the electrostatic charge generating device 12 is turned ON, based on the paper sheet feeding command. When the overlapping conveyance error of the paper sheet 2 occurs as shown in FIG. 7, the regular paper sheet 19a to be conveyed regularly is adsorbed by the electrostatic force generated by the electrostatic charge generating device 12. On the other hand, associating with the action for adsorbing the regular paper sheet 19a toward the electrostatic charge generating device 12, the leading edge portion of the overlap paper sheet 19b is separated from the regular paper sheet 19a by the gravity of the overlap paper sheet 19b. The electrostatic force generated by the electrostatic charge generating device 12 is set at a weak force to such an extent that the electrostatic force is barely stronger than the gravity force, and therefore, hardly impedes the conveying operation to be conducted by the pair of conveyance rollers 5 for conveying the regular paper sheet 19a. As a result, associating with the conveying action conducted by the pair of conveyance rollers 5, the regular paper sheet 19a to be conveyed regularly is guided by the upper guide plate 11b and the lower guide plate 15b so as to pass through the conveyance path 17, and arrives at the pair of registration rollers 7. Then, the regular paper sheet 19a is conveyed to the image forming section by the pair of registration rollers 7, in order to apply a certain image forming operation, such as a copying operation of the original document, etc., to the regular paper sheet 19a. On the other hand, the overlap paper sheet 19b passes through the overlapping conveyance path 18, and is detected by the overlap paper sheet detecting sensor 10, and passes through the pair of conveyance rollers 14, in order to stack it onto the overlap paper sheet stacking tray 16. Incidentally, in the example mentioned in the above, although the electrostatic charge generating device 12 is employed for adsorbing the overlap paper sheet 19b, the suction fan 13 is also applicable for this purpose, instead of the electrostatic charge generating device 12.
As mentioned in the above, according to the separating conveyance apparatus set forth in the Patent Document 1 (namely, Tokkaihei 6-32498, Japanese Non-Examined Patent Publication), the paper sheet separating action is achieved by conveying the necessary paper sheet while adsorbing it, and on the other hand, dropping the overlap paper sheet by using the gravity force caused by its own weight. However, the dropping action by the gravity force caused by its own weight cannot be expected with respect to overlapping paper sheets caused by the frictional electrification, a reuse paper sheet, a thick paper sheet, or the like, and sometimes, such the overlap paper sheet would be conveyed into the regular conveyance path.
In addition, since the abovementioned separating method utilizes the action of the gravity, the application of the method is limited to only a horizontal conveyance structure.